Circadian rhythms and the effect of glucocorticoids on expression of the clock gene period1 in canine peripheral blood mononuclear cells

Circadian rhythms have a periodicity of approximately 24 h and, in mammals, are regulated by clock genes. In this study, expression profiles of clock genes (per1, per2, clock, bmal1 and cry1) were investigated over a single 24 h period by real-time PCR in peripheral blood mononuclear cells (PBMCs) of healthy dogs and canine PBMCs treated in vitro and in vivo with glucocorticoids. Only per1 mRNA exhibited daily rhythms in canine PBMCs. Canine PBMCs cultured with dexamethasone in vitro had dose- and time-dependent increases in per1 mRNA expression. Intravenous injection of dexamethasone increased expression of per1 in canine PBMCs in vivo. Rhythmic expression of per1 in PBMCs could be used as a molecular marker for monitoring circadian rhythms and the effects of drugs on clock genes in dogs.